This invention relates generally to internal combustion engines and more particularly to a stratified scavenging two-stroke internal combustion engine.
Generally, in a so-called stratified scavenging two stroke internal combustion engine a scavenging air supply is introduced into a combustion chamber of the engine after a combustion event has occurred and before a fuel and air mixture is delivered from a crankcase chamber of the engine to facilitate exhausting the combusted gas from the combustion chamber and to provide some air to facilitate combustion of a subsequently delivered fuel and air mixture. During rapid acceleration of the engine, the scavenging air enters the combustion chamber at a high flow rate which tends to dilute the fuel and air mixture making it overly lean and thereby materially deteriorating the acceleration, performance and stability of the engine.
When the scavenging air supply is limited or throttled during rapid acceleration of the engine, the stability of the acceleration of the engine is improved because dilution of the fuel and air mixture is prevented but the maximum power output of the engine is significantly reduced. If the fuel mixture passage is widened or enlarged, the requirements for acceleration and maximum power output can be satisfied, but there is an increased and unacceptably high level of exhaust emissions from the engine.
A two-stroke internal combustion engine having an air control which controls scavenging air flow during rapid engine acceleration to optimize the acceleration and maximum power output of the engine while maintaining low exhaust emissions from the engine. Desirably, the air control may comprise a valve that throttles the air passage to one half or less of its total flow area at a medium engine load or less and completely or fully opens at a medium engine load or more of the engine. Normally, the air control valve opens in unison with the throttle valve, but during rapid acceleration of the engine the air control valve opens later or more slowly than the throttle valve to control the supply of scavenging air to the combustion chamber of the engine thereby enhancing rapid acceleration of the engine. The air control valve eventually fully opens to increase the maximum power output of the engine and the fuel mixture passage need not be widened to avoid excessive exhaust emissions.
In one form, the air control may be a butterfly or disk type valve driven for rotation by the rotation of the throttle valve through a linkage. In another form, the air control may be a plunger type valve biased by a spring to delay its opening upon rapid acceleration of the engine. In yet another form, the air control may comprise a read type valve. In yet another form, the air control comprises an air passage between the carburetor and engine which is longer than the fuel and air mixture passage so that upon rapid engine acceleration, which tends to draw increased air into the combustion chamber, the scavenging air has a longer path to travel than the fuel and air mixture. Hence, less air is drawn into the engine during rapid acceleration to prevent undue dilution of the fuel mixture in the combustion chamber and enable smooth, stable acceleration. In any form, the flow of air to the combustion chamber during rapid acceleration of the engine is controlled to limit the air flow into the combustion chamber and thereby provide a desired fuel and air mixture suitable to enable rapid acceleration without loss of power output from the engine and without increasing the exhaust emissions of the engine.
Objects, features and advantages of this invention include providing an engine which provides a scavenging air supply to the engine, controls the flow rate of scavenging air at least during rapid engine acceleration, enables smooth, stable and rapid engine acceleration, permits a high maximum engine power output, has relatively low exhaust emissions, improves the responsiveness of the engine, is of relatively simple design economical manufacture and assembly, and in service has a long and useful life.